Temperature-dependent oxidation behavior of Inconel 718 under cyclic conditions

This study investigates the temperature-dependent cyclic oxidation behavior of Inconel 718 superalloy by combining experimental characterization with Thermo-Calc-based thermodynamic predictions. The samples were exposed to 25 oxidation cycles at 550 °C, 650 °C, and 750 °C, with each cycle consisting of 1 h exposure followed by cooling to room temperature. The oxidation kinetics showed a rapid initial mass gain followed by a slower quasi-steady regime, and the total mass gain increased with temperature, reaching its highest value at 750 °C. XRD, SEM–EDS, and XPS analyses revealed the formation of protective oxide scales mainly consisting of NiO, Cr-containing oxides, and possible Ni–Cr spinel-type oxides, with more developed multilayer oxide features at 750 °C. Thermodynamic predictions supported the experimentally observed phase stability and oxide formation tendencies. The combined results indicate that oxidation resistance IN-718 is governed by the temperature-dependent evolution of diffusion-controlled oxide layers and elemental redistribution across the oxide/metal interface. The novelty of this study lies in correlating cyclic oxidation kinetics with microstructural, chemical-state, and thermodynamic evidence to clarify protective oxide scale evolution IN-718 under repeated thermal exposure.